Flux Growth of Single Crystal Lead-Titanate and Property Measurements
Suchicital, Carlos Tres Ayala
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https://hdl.handle.net/2142/71714
Description
Title
Flux Growth of Single Crystal Lead-Titanate and Property Measurements
Author(s)
Suchicital, Carlos Tres Ayala
Issue Date
1988
Doctoral Committee Chair(s)
Payne, David A.
Department of Study
Ceramics Engineering
Discipline
Ceramics Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
This thesis is concerned with the crystal growth of lead titanate, and the determination of basic electrical, mechanical and optical properties. Of particular concern is the disruptive phase transformation at approximately 500$\sp\circ$C, and the attainment of large equidimensional crystals free of defects. A flux method was developed for the growth of single crystals at reduced temperatures. High quality crack-free crystals were obtained below the transformation temperature, with well developed (100), (010) and (001) faceted faces.
High temperature x-ray diffraction and optical microscopy methods were used to determine volume and shape changes which occurred on heating through the polar/non-polar transformation. Microcracks were observed to initiate and form at domain interceptions on cycling through the transformation temperature. A transformation strain energy of 32.4 kJ/mole was determined by differential scanning calorimetry, and the thermal hysteresis was 13$\sp\circ$C.
Room temperature microindentation measurements determined hardness anisotropies for tetragonal lead titanate. In addition, crack initiation and growth was observed by optical methods. A model is proposed to account for plastic deformations, and the propagation of lateral cracks with median/radial distributions. The results are interpreted in terms of mechanical properties and fracture behavior of lead titanate.
Chemical analyses and infrared spectroscopy measurements determined the characteristics of flux grown crystals. The room temperature resistivity was 10$\sp $ $\Omega$-cm, which was four orders of magnitude greater than any other known reported values. Electrical measurements were determined for oriented single crystals and the properties were analyzed by impedance and susceptance determinations as a function of temperature and frequency. The weak field dielectric constants at room temperature and 1 kHz, were K$\sb \sp{\rm T}$ = 225 with K$\sb{33}\sp{\rm T}$ = 134. From resonance behavior characteristics, the piezoelectric coefficients were estimated to be d$\sb{33}$ = 30 pC/N and g$\sb{33}$ = 24.4 $\times$ 10$\sp{-3}$ m$\sp2$/C. Data are reported for compliance measurements.
The thrust of the thesis was to develop a method for the crystal growth of large equidimensional crystals of lead titanate, and the determination of basic property measurements. Emphasis was placed on structural factors which related to microcracking, especially on cooling into the anisotropic state.
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